U.S. patent number 5,402,493 [Application Number 07/970,141] was granted by the patent office on 1995-03-28 for electronic simulator of non-linear and active cochlear spectrum analysis.
This patent grant is currently assigned to Central Institute For The Deaf. Invention is credited to Julius L. Goldstein.
United States Patent |
5,402,493 |
Goldstein |
March 28, 1995 |
Electronic simulator of non-linear and active cochlear spectrum
analysis
Abstract
A model simulating cochlear spectrum analysis is disclosed which
includes a pair of matched all pole lattices interconnected by a
plurality of tip couplers providing non-linear distributed
bilateral signal processing. One of the lattices along with the tip
couplers corresponds to the organ of Corti found in the cochlea and
the second lattice corresponds to the basilar membrane also found
in the cochlea such that the model provides a striking resemblance
in structure to the physical properties of the cochlea itself. With
the cochlea model disclosed, distortion products and otoacoustic
emissions are simulated. An intermediate model is also disclosed
which provides bilateral signal processing but lacks distributed
amplification.
Inventors: |
Goldstein; Julius L. (St.
Louis, MO) |
Assignee: |
Central Institute For The Deaf
(St. Louis, MO)
|
Family
ID: |
25516501 |
Appl.
No.: |
07/970,141 |
Filed: |
November 2, 1992 |
Current U.S.
Class: |
381/61; 381/60;
381/320 |
Current CPC
Class: |
H04R
25/505 (20130101) |
Current International
Class: |
A61N
1/36 (20060101); H04R 25/00 (20060101); H04R
025/00 () |
Field of
Search: |
;128/746 ;73/585
;381/60,68.2,68.4 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Introduction to Distributed Amplification by Harry Stockman, Second
Editioin, 1956, Preface p. vii. .
Article entitled Digital Signal Processing With the TMS320C25 by
Rulph Chassaing et al, published by Wiley-Interscience Publication,
1990, pp. xiii-14. .
Article entitled Micromechanical Models of the Cochlea by Jont
Allen et al, published in Physics Today, Jul. 1992, pp. 40-47.
.
Article entitled Adequacy of auditory models to predict human
internal representation of speech sounds by Oded Ghitza, published
in the J. Accoust. Soc. Am. 93 (4), Apr. 1993, pp. 2160-2171. .
Article entitled Electronic Amplifier Circuits - Theory and Design,
by Joseph M. Pettit et al, published by McGraw-Hill, New York,
1961, pp. 147-163..
|
Primary Examiner: Isen; Forester W.
Attorney, Agent or Firm: Rogers, Howell & Haferkamp
Claims
What is claimed is:
1. In a sound analyzer having means for receiving a complex sound
input comprised of a plurality of frequencies and means for
producing an output representative of the frequency response of a
human ear, the improvement comprising said output means having
means for producing acoustical distortion products as demonstrated
to emanate from the human ear.
2. The sound analyzer of claim 1 wherein said output means has
means for producing spontaneous emissions as demonstrated to
emanate from the human ear.
3. The sound analyzer of claim 2 wherein said output means has
means for producing an output which simulates the non-linear
interaction between said spontaneous emissions and external sounds
as demonstrated to occur in the human ear.
4. In a sound analyzer having means for receiving a complex sound
input comprised of a plurality of frequencies and means for
producing an output representative of the frequency response of a
human ear, the improvement comprising means for varying the
sensitivity of said analyzer in response to non-linear bilateral
signal processing between said input and said output with respect
to each of said plurality of frequencies of said complex sound
input to thereby adjust said output.
5. The sound analyzer of claim 4 wherein said output comprises a
plurality of discrete outputs, each of said outputs being
representative of said frequency response at a pre-selected
frequency, and said sensitivity varying means comprises varying the
number of discrete outputs over a particular frequency range.
6. The sound analyzer of claim 5 wherein said sensitivity varying
means further comprises means associated with each of said discrete
outputs for varying the strength of said output.
7. The sound analyzer of claim 6 further comprising means for
selectively attenuating the output at all frequencies.
8. In a sound analyzer having means for receiving a complex sound
input comprised of a plurality of frequencies and means for
producing an output representative of the frequency response of a
human ear, the improvement comprising a non-linear, additive,
directional wave amplifier means so that said plurality of
frequencies may be added in proper time sequence at different
locations within said output producing means, said amplifier means
being connected between said receiving means and said output
producing means.
9. The sound analyzer of claim 8 wherein said amplifier means
comprises a pair of matched all pole lattices.
10. The sound analyzer of claim 9 wherein said amplifier means
further comprises a plurality of non-linear couplers interconnected
between said pair of lattices.
11. The sound analyzer of claim 10 wherein said output means
comprises a plurality of taps into one of said lattices, each of
said taps providing an output at a particular frequency.
12. The sound analyzer of claim 11 further comprising means for
selecting the number of taps and means for selecting the frequency
of the output at each of said taps to thereby adjust the
sensitivity and frequency range of said sound analyzer.
13. The sound analyzer of claim 12 wherein one of said lattices has
means for propagating a signal in two directions therethrough.
14. The sound analyzer of claim 13 wherein said one lattice having
means for propagating a signal in two directions is closer to said
input than said other lattice.
15. The sound analyzer of claim 14 wherein said lattice having a
plurality of taps utilizes propagation of signals in only one
direction.
16. The sound analyzer of claim 15 further comprising a
variable-gain preamplifier interconnected between said
lattices.
17. The sound analyzer of claim 16 further comprising an outer ear
circuit connected to an inner ear circuit, with the output of said
inner ear circuit being connected to each of said lattices.
18. In a sound analyzer having means for receiving a complex sound
input comprised of a plurality of frequencies and means for
producing an output representative of the frequency response of a
human ear, the improvement comprising means for processing signals
in both directions between input and output.
19. The sound analyzer of claim 18 wherein said signal processing
means includes means for non-linearly amplifying said signals.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
Many researchers, including the inventor herein, have spent many
years trying to understand the biophysical mechanisms of the human
ear to understand how the human ear works and also to help in
developing a module, which may be physically constructed, which
duplicates or simulates the operation of the ear. Many theories and
models have been developed over the years which have progressed
this development. The inventor herein has previously developed a
biophysical model (Goldstein, J. L. "Modeling rapid waveform
compression on the basilar membrane as
multiple-bandpass-nonlinearity filtering", Hearing Research 49,
39-60) which sought to explain the biophysical mechanisms of the
ear in terms of a multiple band pass non-linear input/output model
for simulating the non-linear basilar membrane response. The
approach in this prior model was to account for non-linear cochlear
phenomena directly in terms of a mathematical model of I/O behavior
rather than treating them as non-linear perturbations from a
physically based linear theory. This basic model, and later models,
incorporate two non-linearly interacting filter systems that
simulate the two distinct non-linear regimes observed in all
non-linear phenomena at low-to-moderate and moderate-to-high
stimulus sound levels. While this prior model and theory
represented a dramatic departure from the prior art in itself, and
helped to advance the work on understanding the ear as it provided
new direction, this model was not a complete answer in that it did
not explain observed phenomena such as distortion products and
otoacoustic emissions, or otherwise provide any understanding of
the operation of the organ of Corti. Furthermore, the model did not
fully address the function of the basilar membrane as the model
structure does not reflect the known biophysical properties of the
cochlea.
With the present invention (See Goldstein, J. L., Changing Roles in
the Cochlea: Bandpass Filtering by the organ of Corti and Additive
Amplification of the Basilar Membrane, paper 4aPP3 at 124th Meeting
of the Acoustical Society of America, November 1992), the inventor
has improved on his earlier model to bring it further in congruence
with the known biophysical mechanisms of the ear, including most
particularly the organ of Corti and basilar membrane, and has in
the process achieved simulation of the heretofore unexplained
distortion product and otoacoustic emissions. In an intermediate
step, the inventor has added bilateral signal processing to his
prior model to more completely simulate the two signaling channels
responsible for the "tips" and "tails" of Cochlear tuning curves.
This bilateral processing potentiates extension of the model to
other phenomena, including combination tones (distortion products)
and otoacoustic emissions. This intermediate step takes advantage
of non-linear feedback while the full invention adds distributed
amplification. This distributed amplification provides for the
non-linear addition of many signals from tip sources which are
believed to function similarly to the organ of Corti. These organ
of Corti filters, or tip sources, are connected at different
locations along a filter-bank spectrum analyzer (a corollary to the
outer hair cells and adjoining structures) and are non-linearly
added through a propagating medium (a corollary to the basilar
membrane) to provide distributed amplification. This model thus
helps explain the non-linear input/output characteristic as
observed by others in the basilar membrane mechanical response in
the human ear.
There are several additional features of the present invention,
including a "zoom" capability, a sensitivity adjustment, and
efferent neural control simulation. As explained in greater detail
below, the present invention includes a pair of matched all pole
lattices with a plurality of tip couplers tapped into each lattice
and interconnecting them at chosen "center frequencies". A scaling
factor, or alpha, may be induced at any frequency to alter the
response at that frequency and thereby match the model's output to
any particular human ear output. Additionally, an efferent bias
control, which is ordinarily set to zero, may also be used to scale
the throughput of any one or more tip couplers to simulate the
brain's ability in humans to "tune out" undesirable sounds or
simulate "listening without hearing" as experienced in humans.
Choosing the number of tip couplers (and hence the length of the
matched lattices), and the "center frequencies" of each of the tip
couplers permits the model builder to focus on any one or more
range of frequencies for measurement with the model. Additionally,
the model accommodates the use of 12,000 tip modules which
corresponds to the full complement of outer hair cells believed to
be contained and operative in the organ of Corti, to thereby
provide a full representation and simulation of the frequency range
of the human ear. As this may be cumbersome or undesirable, a fewer
number of tip couplers may be used and may be focused over a chosen
portion of the frequency range of hearing to thereby minimize cost
and complexity of the model while still simulating with great
accuracy the desired response frequencies.
While the principal advantages and features of the present
invention have been described above, a more complete and thorough
understanding of the invention may be attained by referring to the
drawings and description of the preferred embodiment which
follow.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram representing the inventor's prior art
model for simulating human ear response;
FIG. 2 is a first embodiment of the invention which includes
bilateral signal processing in a model for simulating human ear
response;
FIG. 3 is a schematic depicting the inventor's interpretation of
the biological function of the cochlea;
FIG. 4 depicts a schematic representation of an idealized example
based upon in-phase addition of apically propagating "tip"
responses;
FIG. 5 is a schematic of the present invention detailing the
non-linear cochlear simulator;
FIG. 6 is a graph detailing the measured response of the present
invention;
FIGS. 7a and 7b are schematic diagrams detailing lattice
construction as utilized in the present invention;
FIG. 8 is a graph providing the relationship between tip coupler
density and tip preamplifier gain; and
FIG. 9 is a partial schematic of the model shown in FIG. 5 and
further detailing the interconnection between the tip line lattice
and tail line lattice through the tip couplers.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
As shown in FIG. 1, the inventor herein has previously developed a
model for explaining and simulating the cochlear response of the
human ear. In essence, the model of FIG. 1 is characterized by a
unilateral non-linear signal processing of two signaling channels
responsible for the "tips" and "tails" well demonstrated in the
literature as being measured in cochlear frequency tuning curves.
Using this prior art, cochlear spectrum analysis would be
approximately simulated by a bank of independent non-linear
filters, each tuned to a different audible frequency. Further
details of the specific operation and functional components of the
model of FIG. 1 are described in the inventor's prior article
referenced above. However, it is important to note that signal
processing occurs from left to right as shown in FIG. 1 and there
is no feedback loop nor counter signal flow demonstrated by the
model. Nevertheless, the model is successful in simulating sound
level dependent non-linear cochlear frequency analysis as measured
in many psycho-physical and biophysical experiments.
The inventor's further work has led to the development of the
present invention which, in its first embodiment, incorporates
bilateral signal processing by the alternate signal paths through
the functions f and f.sup.-1. This bilateral signal processing
potentiates extension of the model such that it can be used to
explain other phenomena not previously explainable with the model
of FIG. 1, e.g. combination tones and otoacoustic emissions. As
shown in FIG. 2, points 2 and 3 may be thought of as taps in a
propagating medium, further identified in later developments as
shown herein as the basilar membrane. The non-linear feedback loop
through which the bilateral signal processing occurs, i.e. through
the alternate branches of f and f.sup.-1, provides non-linear
addition of a signal from the unilateral tip source at point 1
therein with a signal on the propagating "tail medium" at point
three as shown therein. With this modification to the model of FIG.
1, spectrum analysis by independent nonlinear filters is retained
and there is no interaction suggested between apically propagating
responses. In other words, the low pass filter H3 admits low
frequency signals through the middle ear and the tuned filter H1
admits sounds at the center frequency .omega..sub.c and its
response is non-linearly processed, as explained, with an output
response filtered through band pass filter H2. Interaction between
non-linear filters tuned to different frequencies is not suggested
or explained in the model and schematic of FIG. 2.
As shown in FIG. 3, the inventor has extended this non-linear
amplification principle to include a basilar membrane as a
propagating medium which allows for the interaction between the
sensed response of organ of Corti filters tuned to different
frequencies. As shown therein, a plurality of tip filters H1 are
each tuned to a different center frequency CF.sub.i which are then
non-linearly coupled for bilateral processing to the basilar
membrane. The measured responses are thus the result of a
distributed non-linear amplifying effect. This bilateral signal
processing is further exemplified by the double headed arrows
connecting the cochlea (comprising the organ of Corti and basilar
membrane) with the middle ear and outer ear. This model closely
parallels the actual physical construction of the cochlea and hence
provides a model for construction of an electronic simulator for
the cochlea. Of course, electronic circuitry simulating the middle
ear and outer ear are well known in the art. See, for example,
Chassaing R. and Horning D. W., (1990) Digital Signal Processing
with the TMS 320C25; and Lin, Kun-Shan, Ed. (1987) Digital Signal
Processing Applications with the TMS 320 Family, Vol. 1. The effect
of bilateral processing is shown in FIG. 6 to bring the response
curve more into conformance with measured response for the ear.
As shown in FIG. 4, an idealized example is presented wherein a
plurality of band pass filters having a center frequency CF.sub.1
provide a response to an input frequency F.sub.S which is then
non-linearly processed and summed along the apex or base, through a
series of low pass filters.
A more physically realizable representation and embodiment for the
present invention is shown in FIG. 5. As depicted therein, a pair
of matched lattices comprising a tip line lattice and a tail line
lattice are interconnected by a plurality of tip modules (as shown
in FIG. 2) to provide non-linear bilateral signal processing
therebetween at different frequency points. The tip line and tail
line lattice are conventional all pole lattices as shown in FIG.
7b. As shown in FIG. 7a, a one pole lattice representing an
idealized section of a non-uniform acoustic tube has F.sub.i and
B.sub.i as its forward and backward waves. A unit delay Z.sup.-1
equals the transit time of the section. K.sub.i is the reflection
coefficient that depends upon the ratio of cross-sectional areas of
the idealized successive sections. For the all pole lattice as
shown in FIG. 7b, and as used as the tip line and tail line
lattices of FIG. 5, the forward delay is eliminated and the
backward delay corresponds to twice the transit time. The scaling
factor for each section is normalized to unity. Except for the
scale factor and delay, the form of the frequency response is
unchanged, as demonstrated therein.
As shown in FIG. 5, the responses interact along the tail line
lattice much as is believed to be the case in the basilar membrane
of the human ear. Similarly, the non-linearly coupled tip line
lattice and differentiator D(Z) provide a phase-matched filter-bank
sound analysis that is believed to simulate the action of the outer
hair cells and adjoining structures comprising the organ of Corti.
Thus, the model, as shown in the preferred embodiment of FIG. 5,
has some correspondence to the physical properties of the cochlea
and hence provide added insight into the actual physical mechanisms
at work in the cochlea.
As shown in FIG. 9, this correlation between the model of the
present invention and the cochlea itself leads to adjustments in
the model which may be used to simulate responses measured in the
human ear. For example, the filter responses of the tip line
lattice must be normalized to the "center frequency" of each tip
filter or tip module. In this event, losses in sensitivity of each
of these tip filters or modules may be simulated by choosing a
scaling factor alpha such that 0.ltoreq..varies..ltoreq.1. This
scaling factor may be used to adjust the output at the "center
frequency", corresponding to the response, as would be the case in
the response of a damaged cochlea. Similarly, efferent neural
control of the tip sensitivity can be simulated by providing a
quiescent bias control at each of the tip modules, as shown. This
efferent neural control is representative of the brain's ability to
suppress the response of the ear to undesirable sounds and to also
simulate the results of inattentiveness, as when a person is
listening but not hearing. Coupling of the backward propagation to
the tip line from the tail line can be controlled by choosing beta
such that 0.ltoreq..beta..ltoreq.1. Similarly, the tip preamplifier
G may have its gain adjusted to correspond to the number of tip
couplers used in implementing the simulator. This is shown in FIG.
8 which allows that number to be as large as the 12,000 outer hair
cells of the organ of Corti. As shown in FIG. 8, 600 represents
five percent of these hair cells. For example, 400 tip couplers can
be uniformly spaced over the whole basilar membrane, whereupon
G=19. Or, the 400 tip couplers can be "zoomed" onto one 5% region,
whereupon G=1. This can result in reduced simulator complexity and
cost in order to provide a model which simulates this response.
The invention was demonstrated using VLSI simulation technology.
The preferred embodiment is the recommended implementation. VLSI
simulation required a powerful general purpose computer, while the
inventor considers DSP technology more practical.
It is understood that other technology may be used to implement the
invention. Also, one of ordinary skill in the art, knowing the
desired non-linear response as included in the tip couplers, could
readily design and implement a custom DSP chip for interconnecting
the two all pole lattices.
There are various changes and modifications which may be made to
the invention as would be apparent to those skilled in the art.
However, these changes or modifications are included in the
teaching of the disclosure, and it is intended that the invention
be limited only by the scope of the claims appended hereto.
* * * * *